Before you put the cable on adjust the tension of the springs.Use your sensibility in your hands to get equal tension on both sides.This way you know the tension is the same on both sides and the cable isnt interfering.Then put in the cable, if you still notice there is more pull on one of the sides, give the springs more tension.(make sure your cable is running smooth)
You could do what TJ says, or just head over to your nearest bike shop and they will know what to do. All they will do is check it out and tell you what to do. Then you do what they say and its done. Its much easier to diagnose the problem and come up with a solution when the object is right there in front of you. Thats why having someone actually looking at it is better and you will get a more accurate answer. I recommend that you hang out at a bike shop and watch what they do to other peoples bikes or fix everything on your bike by hand, so you understand everything on your bike and can do your own maintainance. Thats what I did and now I completely understand my bike. In fact im actually replacing a broken bb cup today. Woo hoo, i finally get to ride after 2 weeks!